CD56, also known as neural cell adhesion molecule 1 (NCAM1), is a type I membrane glycoprotein involved in cell-cell and cell-matrix adhesion. Its extracellular domain has five IgG-like domains at the N-terminus and two fibronectin type III domains in the membrane-proximal region. It has been reported that the function of CD56 is important for cell migration and tumor metastasis. The two domains are thought to have different functional roles, with the IgG-like domains involved in homophilic interactions with other CD56 molecules, either on the same cell or a neighboring cell (Jensen and Berthold, Cancer Lett 258(1):9-21, 2007). The fibronectin type III domains are believed to mediate signaling to downstream proteins. CD56 is over-expressed in nearly all neuroblastomas (Wachowiak et al., Pediatr Surg Int 24(12):1361-1364, 2008), 98% of small cell lung cancers (Zheng and Maleki, Acta Cytol 57(3):281-290, 2013; Whiteman, et al., MAbs 6(2):556-566, 2014) and 78% of multiple myelomas (Lutz and Whiteman, MAbs 1(6):548-551, 2009). In addition, some ovarian cancers also exhibit elevated CD56 levels (Ohishi et al., Gynecol Oncol 107(1):30-38, 2007).